This invention relates, in general, to timers for electrically energized apparatus and, in particular, to a controller for initiating operation of a tape recorder at a preset time, and for terminating its operation in response to a reduction in power consumption by the recorder.
The use of a timer, in the form of a clock, in connection with home entertainment products is well known. For example, the conventional clock radio immediately suggests itself. The timing arrangement for clock radios, however, is usually one of two varieties, an arrangement which turns on the radio at a preset time and then permits the radio to play indefinitely, or an arrangement which turns on the radio at a preset time and thereafter turns it off, usually one, or more hours later. Insofar as clocks for radios are concerned, the industry has, of late, been particularly attracted to the digital type clock because of the accuracy with which it can be set. However, these digital clocks are commonly programmed for 1 hour of "ON" time.
It is also recognized that automatic timers are commonly used for switching lights on and off in a temporarily unoccupied home and, that such a device could be used to turn on a radio, a television receiver, or a tape recorder at a predetermined time and to turn the instrument off at a later time. In view of their design function, i.e., a time controlled light switch, the degree of accuracy afforded by such timers, insofar as turn on and turn off time is concerned, is nominal since it matters little exactly what time lights are turned on or off in the home.
As will be shown, the control of a video tape recorder occasions special timing considerations which, at best, can only be partially resolved by the aforementioned prior art timers. In this regard, while one prior art timer would turn the video recorder on and off, it would do so with questionable accuracy from a time standpoint; another timer may turn the recorder on with acceptable accuracy, but the recorder would be turned off one hour later, or it would remain energized until the preset hourly increments passed.
In the case of a video tape recorder, however, a presettable time is extremely critical for several reasons. First of all, if it is desired to record an upcoming television program via a preset timing arrangement, the turn on time must be extremely accurate if one is to be assured of recording the beginning of the program. On the other hand, the turn off time may not be so critical so long as the recorder remains energized until the tape is exhausted. This latter situation can be tolerated because any material stored subsequent to the conclusion of the deisred program can be readily erased.
As another example of prior art practice, timing control in a known video tape recorder has been resolved in the following manner. A built-in timer initiates the recording mode. However, the timer has a multiple hour "ON" period intentionally designed to accomodate the longest playing tapes available plus a substantial safety factor. In this particular recorder, there is also provided sensing circuitry which monitors the tape so that as the end of the tape approaches the drive capstan, a control signal is derived by a sensor which turns off the capstan drive motors. However, the signal processing and amplifier circuitry remain energized until the completion of the timer's multiple hour "ON" period. This, obviously, results in unnecessary operation of some of the recorder circuits as well as an undesirable waste of electrical energy.
Finally, it is appreciated that the circuitry of the recorder itself can be revised to adopt presettable timing circuitry of such sophistication as to resolve the problems posed herein. This, of course, is attractive insofar as to-be-manufactured units are concerned, but it is an impractical remedy for the multitude of recorders already in the field.